168 



Mr. T. Hopkins on the Causes of the 



names. I shall therefore call the Colonel's " the temperature 

 theory" and the other, " the condensation theory" Both of 

 these rest on alterations of temperature ; but the former de- 

 pends on the temperature found by thermometric measure- 

 ment near the earth's surface, and the latter on the temperature 

 which must be produced by condensation of vapour in a 

 higher part of the atmosphere, of which we have no direct 

 measure. 



The semi-diurnal fluctuations of the barometer are the 

 greatest within the tropics ; and as details of those at Bombay 

 have not yet been published, we will proceed to examine ac- 

 counts furnished by Kaemtz in his valuable work on Meteo- 

 rology. In page 248 of that work we have the following tables 

 of the hourly heights of the barometer: — 



Table I. 



Mean height of the barometer expressed in millimetres for all 

 hours, and in different places. 



From an examination of this table, it will be seen that the 

 fluctuations are the greatest within the tropics, and they 

 diminish, though not invariably, with the increase of latitude. 



